Question

when heat is being supplied to the solid then what does the heat energy to do the particles of solid

Answer 1

Heat increases the kinetic energy of the particles and as a result the particles of a particular solid starts moving woth higher speed which results in the breaking of strong attraction forces between the particles of solid. As the forces of attraction become less the particles become more free to move and hence gets converted into liquid

Answer 2

When the heat is supplied then this heat is used to overcome the force of attraction between the particles
During this period the temperature remains the constant but the heat is aquired by particles in the form of Latent heat